1. Field of the Invention
The present invention relates to an ignition and injection control system for an internal combustion engine suitable for use in a vehicle.
2. Description of Related Art
Conventionally, an ignition control system executes a multiple electric discharges operation. In the multiple electric discharges operation, a plurality of discharges are carried out during one engine combustion cycle. For executing the multiple discharges, for example, an ECU outputs an ignition signal IGt to energize and de-energize the primary coil of an ignition coil repeatedly. Thereby, high voltage is introduced in the secondary coil of the ignition coil, and the ignition coil multiply discharges.
The above described multiple discharges operation will be explained in more detail with reference to FIG. 14.
According to the example in FIG. 14, when a gasoline injection type internal combustion engine cold starts, ignition timing thereof is retarded to 100 CA after compression top dead center, and multiple discharges operation discharging five times is executed. Each discharge interval and discharge period are fixed. The discharge interval is set to 1 ins, and each discharge period is set to 0.4 ins. Here, the last (fifth) discharge period is not determined. The engine rotation number is set to 1200 rpm.
When the ignition signal IGt falls down, primary electric current i1 in the ignition coil is shut off, and secondary electric current i2 and secondary voltage V2 are introduced as shown in FIG. 14. Further, as the multiple discharges operation proceeds, the primary electric current i1, the secondary electric current i2, and the secondary voltage V2 change as shown in FIG. 14.
Here, the product of secondary electric current i2 and secondary voltage V2 corresponds to energy density. The energy density reduces as the number of discharges is increased. Since the product of energy density and discharge period corresponds to the discharge energy amount, the discharge energy amount for each discharge reduces as the discharge is repeated. However, the required energy amount for introducing a required spark at each discharge gradually increases. The required energy amount is denoted by slant lines area in FIG. 14. According to experiments conducted by the inventors, when the air-fuel ratio (A/F) of an air-fuel mixed gas is 17, the required discharge energy is 3.5 mJ at the first discharge. The required discharge energy increases as the discharge is repeated, and the discharge energy reaches 9.3 mJ at the fifth discharge. Here, the required energy density is 22 mJ/ms at the first discharge, and is 25 mJ/ms at the fifth discharge.
As is understood from the experiments, as the discharge is repeated, the energy amount introduced by discharge becomes smaller than the required energy amount. Thus, the multiple discharges operation cannot be executed.
An engine control system calculates fuel injection amount and ignition timing. The engine controller outputs an injection signal for each cylinder into an injection operating circuit, and outputs an ignition signal for each cylinder into an ignition operating circuit, for introducing a spark discharge at each ignition plug.
However, the ignition operating circuit and the injection operating circuit are independently formed and arranged far from each other. Thus, even when there is a function device commonly used for both circuits, the function device cannot be shared from a circuit arrangement standpoint, thereby enlarging the circuit scale and increasing the manufacturing cost.
According to the conventional engine control system, the number of signal lines, which lead ignition and injection signals from the engine control computer to each cylinder, is large. Thus, a wide wiring space is needed, and the arrangement of the signal lines becomes complicated, thereby increasing the manufacturing cost.
According to the conventional engine control system, a combustion sensor is provided in each cylinder, thereby increasing the manufacturing cost.
Coils in the ignition operating circuit and the injection operating circuit discharge remaining magnetic energy just after the coils are de-energized. However, the energy is emitted as heat and is not effectively used.